EF2 tornado, Pella to Brooklyn, Iowa, September 30, 2007

1. EF065 to 85 mph

   Light damage. Surface peeled off some roofs, gutters and siding damaged, branches broken, shallow-rooted trees pushed over.

2. EF186 to 110 mph

   Moderate damage. Roofs badly stripped, mobile homes overturned or badly damaged, exterior doors lost, windows broken.

3. EF2111 to 135 mphthis tornado

   Considerable damage. Roofs torn off well-built houses, frame homes shifted on their foundations, mobile homes destroyed, large trees snapped or uprooted, cars lifted off the ground.

4. EF3136 to 165 mph

   Severe damage. Whole stories of well-built houses destroyed, large buildings badly damaged, trains overturned, trees debarked, heavy cars lifted and thrown.

5. EF4166 to 200 mph

   Devastating damage. Well-built houses leveled, structures with weak foundations moved some distance, cars thrown and large missiles generated.

6. EF5over 200 mph

   Incredible damage. Strong frame houses swept off their foundations, car-sized missiles thrown more than 100 meters, steel-reinforced concrete badly damaged, high-rise buildings deformed.

7. Unrated

   The survey recorded a tornado but could not put a number on it, most often because it crossed open country and damaged nothing a rating can be read from.

Rating

EF2

Date

September 30, 2007

Touchdown

6:26 PM CDT (23:26 UTC)

Lifted

6:51 PM CDT (23:51 UTC)

On the ground

25 minutes

Path length

21.9 miles (35.2 km)

Path width

1,250 yards (1143 m)

Deaths

0

Injuries

0

Property damage

$4.1 million

Crop damage

$1,850,000

Counties

Marion, Mahaska, Jasper and Poweshiek counties

Touchdown point

41.463, -92.872

Lift-off point

41.700, -92.600

Record number

0709301726-01

A very dynamic weather system moved into Iowa during the afternoon of the 30th. The system was more reminiscent of what one would expect in April or May. A close upper level low pressure, negatively tilted, lifted northeast through the central U.S. The structure was very classic in appearance with a well defined comma cloudy, dry slot, and warm conveyor in place. By the early evening, the surface low became stacked with the upper low and was located over eastern Nebraska. A defined dry line extended south-southeast out of the low. Surface temperatures warmed into the mid 70s to mid 80s ahead of the low, with dew points in the mid to upper 60s. Dew points behind the dry line dropped into the upper 30s to mid 40s. The airmass became unstable by the late afternoon with CAPE values around 1000 J/kg and lifted indices in the -2 to -4 C. range. Strong dynamics were in place with a 90 kt mid level jet in place, a low level jet of 60 to 70 kts, and an effective shear of 45 to 55 kts. The freezing level was quite high ahead of the approaching low and was between 13,000 and 14,000 feet. The high freezing level, combined with the limited CAPE of 100 to 200 J/kg in the -10 to -30 C. layer of the atmosphere, limited hail production. The downdraft CAPE was in the 600 to 1000 J/kg range, with an LCL of about 1250 meters. Thunderstorms formed in two locations. The first was along the east edge of the dry slot across Kansas. These storms became severe and lifted northeast quite rapidly into southern and central Iowa. Spotty wind damage was reported and one of the storms dropped one inch diameter hail in Marion County. The storms became tornadic as the moved into central Iowa. During the evening of Sunday 30 September 2007 two tornadoes struck portions of Marion, Jasper, Mahaska, and Poweshiek Counties. The first tornado produced EF0 to EF2 damage along its track and was rated EF2 on the Enhanced Fujita Scale with maximum winds of 125 mph. The track was 22 miles in length from 4 miles northeast of Pella to 1 mile north of Interstate 80, 2 miles west of Malcom. Much of the track was three to five tenths of a mile wide, but as wide as seven tenths of a mile at times. The second, shorter and weaker tornado was 5 miles in length and rated EF1 on the Enhanced Fujita Scale. The track began just south of Highway 6, 2.75 miles northwest of Malcom with a maximum width of 150 yards narrowing to 25-50 yards. The storm hit a farmstead just east of 110th street producing EF1 damage with speeds just under 100 mph. The tornadoes caused extensive damage on a farmstead near Malcom with three barns totally destroyed. The barns were 20 by 30 feet, 20 by 40 feet, and 60 by 100 feet. In addition, numerous other damage reports came in from along the track. Fortunately, there were no deaths or injuries from the tornadoes. Thunderstorms also formed close to the upper low center on the nose of the dry punch. There were several reports funnel clouds, along with spotty reports of high winds and hail. A storm chaser confirmed a tornado touchdown 2 NNW of Lytton in Sac county and was on the ground until 4 W of Jolley in Calhoun county. The tornado was in open country and was a small EF0 tornado. One inch diameter hail fell in Sac County, with numerous reports of pea to marble size hail.

Tornado touched down in Marion County, then tracked northeast into Mahaska County.

Tornado moved into Mahaska County from Marion County, then continued northeast into Jasper County.|

Tornado moved into Jasper County from Mahaska County, then continued northeast into Poweshiek County.|

Tornado moved into Poweshiek County from Jasper County. It lifted west of Malcom.|

The second tornado touched down northwest of Malcom. This tornado was on the ground for about 5 miles before lifting north of town.

From NOAA NCEI's Storm Events Database, the narrative the local forecast office wrote for Storm Data.

5 minutes of warning. NWS DMX issued a tornado warning for this county at 23:21 UTC, 5 minutes before the tornado touched down, in force until 23:26 UTC.

The county was under a tornado watch, issued at 20:34 UTC and running to 01:00 UTC.

Every warning and watch covering the touchdown point that day, from the Iowa Environmental Mesonet's archive of National Weather Service products. Lead time is measured from the issue of the warning in force to the touchdown time in the database, both of which were recorded to the minute by different people.

The Storm Prediction Center had this point in a Slight Risk, with a 0.05 chance of a tornado within 25 miles. The outlook in force was issued at 19:52 UTC.

SPC's Day 1 convective outlook as it stood when the tornado began, read at the touchdown point. The same archive is on the radar archive.

The radiosonde launches on either side of the tornado, from the nearest station that was launching then, drawn and analyzed the way Storm Lab does: the same diagram, the same parcel and shear definitions SPC's mesoanalysis uses.

The Des Moines radar (KDMX), 84 km away, was scanning. The volume nearest the touchdown began at 23:25 UTC.

Open the radar archive at this moment, over the track

Reflectivity and velocity, decoded from the Level II archive in the browser. Volumes take a few seconds to open the first time.

Local storm reports within 60 km of the path, in the three hours either side.

From the Iowa Environmental Mesonet's archive of National Weather Service local storm reports.

The live radar over the trackEvery 2007 tornado in IowaEvery tornado in Iowa since 1950Warnings in force in Iowa nowThe forecast where you are

5 more were confirmed in the United States that day.

Ratings are the survey's, read off the damage rather than measured; the rating scale is above. Tornado counts rise through the record as reporting improved, so a year in the 1950s is not comparable with one today except for the strongest tornadoes, which were always noticed.

NOAA Storm Prediction Center tornado database, 1950-2025, the official record kept by NOAA's Storm Prediction Center.